Memory is a cornerstone ability upon which we build knowledge of ourselves and the world around us. Failures in memory, no matter how small, can significantly impact life success and mental health. A large body of research exists regarding the neural bases of memory in adults. This work indicates episodic memory relies on a distributed network of brain regions within temporal, parietal and prefrontal cortices, with the hippocampus playing a critical and irreplaceable role. In contrast, very few studies have examined neural mechanisms underlying memory development in early childhood. This is particularly unfortunate as behavioral research suggests this is a time of significant and rapid development in episodic memory. Additionally, neuroanatomical data from non-human primates have shown that structural development of the hippocampus continues at least through the 5th year postnatally. Although this finding has been theoretically linked to functional development and improvements in behavioral memory performance, it has not yet been examined empirically. Thus, despite all we know about memory processes and associated neural circuitry in adults, the systematic study of its functional maturation early in life is notably absent. This not only poses a gap in scientific understanding but also a barrier to development of intervention techniques that would facilitate or improve memory in those at-risk for impairment. The goal of this proposal is to characterize changes in the structure and function of the hippocampally-mediated episodic memory network during early childhood, when gains in episodic memory are greatest. The primary hypothesis is that episodic memory development results from changes in the hippocampus and its progressive, integrative participation and segregation with cortical areas. In order to test this hypothesis, we will 1) determine how changes in sub regions of the hippocampus contribute to age-related improvements in memory ability during early childhood, 2) determine how the hippocampus becomes integrated with cortical areas to establish a mature memory network and stabilize memory performance in early childhood and 3) identify neural changes that precede behavioral improvements in episodic memory, which will serve as targets for memory intervention in early childhood. To achieve this goal, we will acquire data from ultra-high resolution structural MRI, high resolution resting-state functional MRI, and behavioral assessments of episodic memory ability from a sample of 175 4-to 8-year-old using a cohort-sequential design. This multimodal and longitudinal approach will allow for the identification of neural trajectories that lead to age- related changes in behavior. Systematic study of memory development in childhood has important implications for understanding memory in general and will provide critical information for targeted intervention (and prevention) strategies for populations at-risk for memory impairment and those diagnosed with neurodevelopmental disorders known to affect the hippocampus and memory.